In turbomachinery such as gas turbine engines, the blades used in the various fan, compressor, and turbine stages of the engine are mounted on the perimeter of metal disks also referred to as wheels. The metal disks are in turn mounted to a rotatable shaft supported on bearings.
During engine operation, the disks are subjected to high loads and high mechanical stress as a result of the centrifugal loading imparted to the disk at the high shaft rotational speeds typical of gas turbine engines. This centrifugal loading causes a radially outward pulling force to be applied, predominately by the blades and outer portion of the disk, to the inner portions of the disk known as the disk hub. As a result of this outward loading on the disk hub, the hub is stretched outward in the form of an expanding hoop, thereby creating substantial stress in hoop direction, better known as tangential stress. In fact, the tangential stress in the bore of the disk typically limits the useful life of the wheel.
To overcome this high hoop loading, and associated stress in the disk hub, the disk hubs are thickened in the axial direction to a point where the cross sectional area of the disk hub is sufficient to carry the hoop loading at an acceptable stress level. An undesirable effect of this disk hub thickening is that the weight of the wheel is substantially increased.
This increased weight results in other undesirable effects. Propulsion gas turbine engines are typically designed to be able to contain within the containment structure of the engine the loss of a blade, or the loss of a portion of the rim of a disk. However, because of the substantial mass of the thickened disk hub, it becomes impractical from a cost and weight perspective to add sufficient armor to be able to contain a ruptured disk. Another effect is that the shaft and the support structure in the engine supporting the shaft must be stronger, and consequently heavier, in order to support the disk with the thickened hub.
Accordingly, a need exists for a turbomachinery disk or wheel that can withstand the centrifugal loads due to high speed operation without requiring extra mass at the base of the wheel.